Water (2.2) Flashcards
Describe the structure of an atom (in terms of protons, neutrons and electrons).
An atom is formed by positively charged quarks (protons), neutrons (neutral); they make up the nucleus. Furthermore, the electrons (negative charge) can be found orbiting in a cloud around the nucleus.
What is the difference between an atom and ion?
Atoms have no net charge because they have equal amount of protons and electrons. If an atom loses or gains an electron, there is an unbalance in the amount of electrons and is now considered an ion.
Gained electron = negative net change
Lost electron = positive net change
Contrast anion and cation.
Anion: negatively charged ion (gained electron)
Cation: positively charged ion (lost electron)
What’s the difference between covalent, ionic, and hydrogen bonds?
Covalent: electrons are shared between two atoms
Ionic: attraction between cation and anion (no sharing of electrons)
Hydrogen bond: not a true “bond,” an attraction between polar molecules: dipole-dipole attraction
Describe the cause and effect of the polar nature of water?
CAUSE: In water, the oxygen has a greater “pull” on the electrons than the hydrogen atoms. As a result, there is unequal sharing of electrons, with the electrons drawn closer to the oxygen.
EFFECT: Because electrons have a negative charge, the unequal sharing within the bonds lead to a separation of positive and negative charge, “partial charges” denoted as S+ and S-.
What is a polar molecule?
Molecule that has regions of slight charge due to the unequal sharing electrons in a polar covalent bond.
Contrast adhesive and cohesive.
Adhesion - water attaching to a non-water structure through hydrogen bonding or attraction to an ionic charge.
Cohesion - water attaching to other water through hydrogen bonding.
Outline an example of the cohesive property of water being of benefit to life
- Water cohesion allows for surface tension. Insects such as the water strider are able to stay on the surface of the water.
- Water cohesion creates a chain of water molecules that allows for the transport of water from the roots to the leaves of plants
- Water cohesion is responsible for the high heat capacity of water, maintaining a relatively stable internal and external environment for living organisms.
Outline an example of the adhesive property of water being a benefit to life.
Along with cohesion, adhesion is needed for water to move from the roots to the leaves of plants. Water sticks to the sides of the xylem wall through adhesion.
Explain three thermal properties of water that are useful to living organisms
Melting and boiling point: water melts at (0 C) and boils at (100 C) at relatively high temperatures for a compound made of such light elements, this is due to the hydrogen bonding between water molecules causing them to stick together and to resist being pulled apart (which is what happens when the ice melts and water boils to become gas). Without this, water would not be liquid over much of the surface of the Earth and we would not have an ocean.
High Specific Heat: it takes a relatively large amount of heat energy to raise the temperature of the water. This is a benefit because the temperature of large bodies of water remains relatively constant, protecting life from possibly lethal temperature fluctuations.
Density: because of the H-bonding structure, solid water (ice) is less dense than liquid water. So, ice floats on top of lakes like a blanket, insulating the living organisms in the lake.
Outline a benefit to life of water’s high latent heat of vaporization
“Heat of vaporization” is a measure of how much energy needs to be added to vaporize water. It takes an unusually high amount of heat energy to vaporize water because hydrogen bonds must be broken in order for water molecules to fly off as a gas. As the water evaporates, the surface left behind becomes cooler. This is called evaporative cooling. It allows organisms to cool with sweating so a consistent body temperature is remained.
Explain why water is a good solvent.
It can form hydrogen bonds with a variety of different substances.
Why is water considered the “universal solvent?”
Because it dissolves more substances than any other liquid.
What molecules are hydrophilic? Explain why.
Ionic and Polar, because they have many polar covalent bonds, therefore, resulting into partial charges, making some areas S+ and others S-
What molecules are hydrophobic? Explain why.
non-polar, non-ionic molecules. They don’t have full or partial charges and therefore can’t react with the water molecules.
